Charles Ellicott Commentary 1 Samuel 15:9

"But Saul and the people spared Agag, and the best of the sheep, and of the oxen, and of the fatlings, and the lambs, and all that was good, and would not utterly destroy them: but everything that was vile and refuse, that they destroyed utterly." — 1 Samuel 15:9 (ASV)

Agag, and the best of the sheep, and of the oxen. —It would seem that Saul carried out the awful curse to the letter (with the exception that he spared the king) in the case of the human beings and the less valuable of their beasts. But covetousness seems to have suggested the preservation of the choicest cattle, and pride probably induced the Hebrew king to save Agag alive, that he might show the people his royal captive.